As far as the "the big three" nutrients are concerned, potassium (K) has recently held a backseat to nitrogen (N) and phosphorus (P) when it comes to media attention and time slots for agronomy seminars.  This is primarily because, unlike N and P, K is not associated with contamination of ground or surface waters when over applications are made.  However, it is not a nutrient that can be neglected, especially in the types of crop rotations we have in Wisconsin where large quantities of corn stover (as silage) and alfalfa hay are removed.  Both crops have high K needs and soils can be quickly depleted if nutrients are not replenished.   

The Perfect Storm

        Events in the past 5 to 10 years have set-up something of an ideal situation to neglect K applications. First, there has been a trend toward more liquid fertilizers being used for corn.  Most liquid fertilizers contain little or no K, so unless additional K is broadcast as a dry fertilizer, deficiencies begin to mount.  Second, we are harvesting crops with inherently higher yields.  The days of 15 tons per acre of corn silage and 3 dry matter tons per acre of alfalfa have passed us by.  It's now common to see 25 ton silage yields and 5 to 6 ton alfalfa yields.  Higher yields equal higher nutrient removal rates......in some cases, a lot higher. 

        Manure management and application rates have changed dramatically in the past 10 years.  This has been for the better.  However, with the elimination of gross over applications of manure to better utilize N and keep P away from the fish, no longer are super high amounts of K "banked" in the soil at levels they once were for future crops.  Finally, there was the great K fertilizer price increase of 2007-08.  For years K (as K₂O) hovered around $0.14 per unit.  Last year, at its high point, the price of K was at or near $0.70 per unit.  It became a tough economic pill to swallow.  Since last year, K prices have retreated but are still much higher than the levels of ten years ago. 

What now?